Whole-Building Hygrothermal Modeling in IEA Annex 41

Annex 41 of the International Energy Agency’s (IEA) Energy Conservation in Buildings and Community Systems program (ECBCS) is a cooperative project on “Whole-Building Heat, Air, and Moisture Response” (MOIST-ENG). Subtask 1 of that project set out to advance development in modeling the integral heat, air, and moisture transfer processes that take place in whole-buildings. Such modeling comprises all relevant elements of buildings: indoor air, the building envelope, inside constructions, furnishing, systems, and users. The building elements interact with each other and with the outside climate. The IEA Annex 41 project runs from 2004–2007, coming to conclusion just before the Thermal Performance of the Exterior Envelopes of Whole Buildings X conference. The Annex 41 project and its Subtask 1 do not aim to produce one state-of-the-art hygrothermal simulation model for whole buildings, but rather aim to stimulate the participants’ own development of such models or advanced use of related existing models. Subtask 1 deals with modeling principles and the arrangement and execution of so-called common exercises with the purpose of gauging how well we can succeed in the modeling. To direct the modeling, free scientific contributions have been invited from specific fields that need the most attention in order to better accomplish the integral building simulations. This paper will give an overview of the advances in whole-building hygrothermal simulation that have been accomplished and presented in conjunction with IEA Annex 41, Subtask 1. In addition, the paper will give an overview of the Common Exercises that have been carried out in the subtask. Based on these two activities, some general experiences are reported about how well we are able today to carry out such advanced modeling, and some recommendations for future developments are indicated.